How much time does a bus lane save?

Everett was the first area community to try out dedicated bus lanes.Josh Reynolds for The Boston Globe/File

For the second straight week, transit commuters on a congested stretch in Roslindale were treated to a dedicated street lane just for MBTA buses on Tuesday, and some happy passengers crowed about the newly-smooth commute into Forest Hills and connections to the Orange Line.

Now the MBTA has the numbers to back up the passengers’ experience.

The agency on Monday released data from Dec. 12, the first of the two days of bus-lane testing, and it showed the one-mile bus trips along Washington Street between Roslindale Square and Forest Hills averaged about four minutes shorter than usual, dropping from 13 minutes to nine.

“It’s substantial for a small corridor,” said Jeff Gonneville, the T’s deputy general manager.

The city used orange cones to block off a parking lane from the start of T service until 9 a.m. on the two Tuesday mornings.

The city chose those days because parking is already prohibited on Tuesday mornings until 7 a.m. because of street sweeping (It also frees the city, for now, from what figures to be the most contentious aspect of the bus lane: the loss of parking for residents, and the prospect of towing cars still in the bus lane.)

The lane is expected to run on a daily basis next spring as part of a longer experiment.

In metro areas across the country, transit planners have been implementing more bus-only lanes, arguing that vehicles carrying high numbers of passengers should get priority on city streets over cars. Improving bus service is also seen as more affordable than building new rail.

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Last year, Everett took the regional lead when it launched a morning bus lane on part of Broadway.

More recently, Somerville began running a bus lane on a short stretch of Prospect Street, headed toward Union Square. Arlington, Cambridge, and Watertown this month won grants to test lanes in their communities.

On the MBTA, buses are second only to the subway in ridership but have the worst on-time performance of the different modes of transit. In addition to pushing for more bus lanes, the T is considering new bus routes and allowing passengers to board through front and back doors to speed up service.